Adding Backbone to the Space Station: 15 Years Since STS-110 (Part 2)

By Ben Evans, on April 16th, 2017

The S-0 truss is maneuvered by Canadarm2 towards its installation position on the U.S. Destiny lab. Photo Credit: NASA

Jerry Ross was already a record-setter before ever launching on his final space mission, STS-110, aboard shuttle Atlantis, on 8 April 2002. For more than three years, he had been the United States’ most experienced spacewalker, with a career total of more than 44 hours of Extravehicular Activity (EVA) across seven excursions. He had participated in Space Station Freedom construction tests in the weeks before the Challenger accident, had saved NASA’s Compton Gamma Ray Observatory and trialed space station equipment in April 1991 and had led the first three spacewalks to assemble the International Space Station (ISS) in December 1998. On his final mission, STS-110, Ross would bring this experience full-circle, by supporting a mission which would allow the nascent ISS to grow still further into the world-class research laboratory that it is today. In doing so, he also set an as-yet-unbroken record as the first human to launch from Earth into space as many as seven times.

Two days after launch, Atlantis and her seven-member crew—Commander Mike Bloomfield, Pilot Steve Frick and Mission Specialists Rex Walheim, Ellen Ochoa, Lee Morin, Steve Smith and Ross himself—docked smoothly at Pressurized Mating Adapter (PMA)-2, at the forward end of the station’s U.S. Destiny lab. They were greeted by incumbent Expedition 4 crew members Yuri Onufrienko of Russia and his NASA crewmates Carl Walz and Dan Bursch, who had not seen another human visitor in almost four months. Yet there was little time for festivities or reunions. The ten astronauts and cosmonauts quickly set to work transferring equipment from Atlantis to the ISS in readiness for four critical spacewalks to install a major piece of hardware onto the station.

As outlined in yesterday’s AmericaSpace history article, that hardware was the 44-foot-long (13.4-meter) S-0 truss segment, which would be attached to the “top” of Destiny and ultimately serve as the centerpoint for the 356-foot-long (108.5-meter) Integrated Truss Structure (ITS). In essence, S-0 would provide an anchoring location for the other truss pieces which would support four gigantic pairs of Solar Array Wings (SAWs), together with batteries, radiators and other subsystems. S-0’s function was more than just a backbone for the ITS: it also facilitated electrical power conversion and acted as a junction through which external utilities could be routed to the space station’s pressurized modules.

Dan Bursch and Ellen Ochoa work at the Robotic Workstation (RWS) during the S-0 installation procedure. Photo Credit: NASA

Ellen Ochoa and Dan Bursch powered up the station’s Canadarm2 and maneuvered it through a “practice run”, putting the 57.7-foot-long (17.6-meter) robotic arm through the same motions which would shortly be required to install S-0 onto the station. “We’re really looking to see if we have the cameras set up the right way, and if we have the infrastructure around Ellen and Dan so that they can do the S-0 install in the time that they think they need to do it,” Bloomfield explained, before the mission. From Ochoa and Bursch’s position, they had no windows, but three monitors, together with two others providing data from the shuttle’s own cameras. “So they’ll have five screens altogether,” continued Bloomfield, “and we’ll feed them all these views to make sure that they can maneuver the arm with S-0 on it, to the correct position.”

Elsewhere, Smith and Walheim were busy setting up equipment in the station’s Quest airlock, from where the four EVAs would take place. They also transferred Smith’s Extravehicular Mobility Unit (EMU) over from the shuttle to the station and hooked it up to airlock systems for interface checks. “The suit that I’ll be wearing is already up there,” Walheim noted in a pre-flight NASA interview, “so the only thing I need to take up there mainly are some of the accessories that I’ll wear. The main thing is my gloves, so we’ll bring my gloves over, put ’em on the suit and we’ll check out the suit and do interface checks with Steve suit, to make sure it’s interfacing with the airlock properly.”

With EVA-1 scheduled to performed by Smith (a Stanford University graduate) and Walheim (a University of California at Berkeley graduate), it was entirely appropriate that the crew was awoken on 11 April by the sounds of the California-Berkeley fight song and by the strains of “All Right Now”, played by Stanford’s band. At 6:30 a.m. EST, working from a Robotic Workstation (RWS) inside the Destiny lab—and supported by additional camera views and verbal cues from Bloomfield and Frick aboard the shuttle—Ochoa and Bursch gently lifted S-0 out of Atlantis’ payload bay. Over the course of about four hours, they maneuvered the 27,000-pound (12,250 kg) truss segment into position on the Lab Cradle Assembly (LCA) atop Destiny.

In the meantime, at 10:36 a.m., Smith and Walheim departed the Quest airlock to begin the first spacewalk of the mission. Timing was critical and it was important to get as much of the S-0 work done early, to allow the spacewalkers to head straight into their first tasks. “We’re running against a thermal clock,” said Bloomfield. “Once [S-0 is] taken out of the payload bay and exposed to the vastness of space, it starts to cool off and there’s about a 28-hour time limit, so basically once we get it in place we have to attach some electrical power to S-0 so that the boxes stay warm.” Additionally, structural strength was needed. Although the LCA provided a grappling claw to offer a semi-rigid configuration, it was imperative for Smith and Walheim to begin the installation of four permanent struts to hold S-0 in place.

As “EV1”, Smith boasted red stripes on the legs of his space suit for identification, whilst Walehim (EV2) wore a pure white suit. The duo attached two forward-facing Module-to-Truss Structure (MTS) struts, allowing them to rotate downward in a V-shape and be attached to the lab. Next, they deployed forward and aft trays of avionics equipment and power, data and fluid cables, together with an umbilical connection from S-0 to the Mobile Transporter. The latter was effectively a “railcar”, enabling equipment to be transported along the entire length of the ITS for future assembly operations. Smith and Walheim returned inside Quest after seven hours and 48 minutes, the second-longest ISS assembly EVA at that time.

Although they were unable to get ahead with a task to install a pair of circuit breakers onto S-0, it was reported that EVA-1 had put STS-110 in pole position and having at least the first two MTS struts in place put S-0 in a safe configuration for EVA-2. Interestingly, it was the first time that Canadarm2 had been used to maneuver a spacewalking astronaut at its tip, with Walheim operating at the end of the arm, as Smith “free-floated” and periodically tethered himself to various locations on the station and shuttle.

The two crews enjoyed a quiet day on 12 April, betwixt EVA-1 and EVA-2, with a light-duty afternoon. This allowed them to get together in the station’s Zvezda service module for a barbecue. “It’s about the time of the rodeo here in Houston,” said Bloomfield, “and both Dan and Carl enjoy the rodeo, so we’re taking up some barbecue beef and some handkerchiefs. Jerry’s a country-western fan, so he’s going to bring some music, and we’re going to try and have our own little party up there.” Making the occasion complete were the crew’s Western-themed bandannas and a culinary concoction from Bloomfield of candy bars and marshmallows and tortillas. “Those were great!” remembered Lee Morin.

Lee Morin, pictured during EVA-2. Photo Credit: NASA

After a day of barbecues and transferring science payloads and other supplies over to the ISS, the second spacewalk got underway at 10:09 a.m. EST on 13 April. With Ross designated “EV3”, clad in a suit with broken red stripes on its legs, and Morin as EV4 with red-and-white hatches on his suit’s legs, the pair had earned a slightly less flattering nickname from their younger crewmates. Both the 54-year-old Ross and the 49-year-old Morin were grandfathers at the time of STS-110 and were correspondingly dubbed the “Silver Team”, on account of their hair color. “They were being nice,” Ross wrote in his memoir, Spacewalker. “It sounded a lot better than the Gray Team or the Balding Team.”

Much of EVA-2 completed what EVA-1 had already begun. Ross and Morin installed two aft-facing MTS struts to securely fasten S-0 onto Destiny, then—despite having to tackle stubborn bolts—fitted backup umbilicals for the Mobile Transporter. With all four MTS struts in place, S-0 was rigidly attached to the space station and able to support its design loads, including the solar arrays. The astronauts returned inside the space station after six hours and 30 minutes, pushing Ross’ experience ever further up the table. By the time he wrapped up his final EVA, he would have accrued 58 hours and 32 minutes across nine spacewalks, positioning himself as the second most experienced spacewalker of all time (after Russian cosmonaut Anatoli Solovyov) and the most experienced U.S. spacewalker and holder of the greatest number of EVAs by a U.S. citizen. He would not lose the U.S. records until February 2007. Even today, Ross remains the third most experienced spacewalker in the world.

By his own admission, records and record-setting were far from Ross’ mind. A mere 24 hours after he completed EVA-2 with Morin, it was time for the third spacewalk of STS-110, performed by Smith and Walheim. The astronauts departed Quest at 9:48 a.m. EST on 14 April and quickly set to work. Their first act was to release the capture claw, which formed the active half of the LCA and which had provided an early semi-rigid structural hold onto S-0. With all four MTS struts now active, the claw was no longer needed.

Next, Smith and Walheim reconfigured electrical connectors to Canadarm2, allowing it to be powered from S-0, rather than from the Destiny lab. After checks of the mechanical arm systems, the spacewalkers removed clamps which held the 1,900-pound (860 kg) Mobile Transporter onto the truss segment. The transporter would ultimately run along rails on the ITS and had the mobility to relocate Canadarm2 and other equipment to ten pre-designated worksites. Moreover, its payload capacity of 46,100 pounds (20,900 kg) allowed it to accommodate large future segments of the ITS itself.

Deferred to the final EVA was the installation of a 14-foot-long (4.2-meter) “ladder”, known as an Airlock Spur, which provided a pathway for future spacewalkers to navigate from the Quest airlock to the S-0 truss. Final diagnostic tests of Canadarm2 meant that this task could not be completed by Smith and Walheim and it was added to the EVA list of Ross and Morin instead. Ending EVA-3 after six hours and 27 minutes, Smith became the second most experienced U.S. spacewalker, after Ross. Even today, Smith maintains a position within the Top Ten most seasoned spacewalkers in the world.

In the meantime, on 15 April, ground controllers and astronauts Frick and Carl Walz commanded the Mobile Transporter to move about 72 feet (22 meters) up and down the S-0 truss, between Worksites 4 and 5. Moving at a glacial pace of less than an inch (2.5 cm) per second, this allowed engineers to evaluate its computers, drive motors, suspension, video and data connections and the S-0 rails. “I don’t want people to get their hopes up too much about a NASCAR race up there on the truss,” Frick quipped, before the mission.

It was the first time that a software-controlled movable robot had been used on an orbiting spacecraft and the Mobile Transporter utilized 20 motors to travel from one point to another on the truss, latching and unlatching itself into place and plugging itself into power sources. Its first run was successful, despite difficulties in latching the transporter down, as the subtle effects of microgravity caused it to slightly “lift” from its tracks. This interfered with magnetic sensors in the transporter itself and prevented them from properly locating iron strips in the aluminum rails.

Finally, at 10:29 a.m. EST on 16 April, Ross and Morin departed Quest for EVA-4. They pivoted the Airlock Spur out to its fully deployed position, then tested electrical switches on the S-0 truss and installed floodlights on the station’s Unity node and Destiny to assist future spacewalkers. For Ross, it was significant, because he knew that it would likely be his last EVA. “The Sun would be setting soon,” he wrote in Spacewalker, describing the final minutes of EVA-4. “I was looking west past the Russian part of the ISS. Below my feet was the Mediterranean Sea and I was traveling at five miles per second to the east. As we passed the fertile, green Nile Delta River, the Sun set in a spectacular display of red, orange, yellow and purple that painted the horizon above the curving silhouette of the Earth.” Ross turned off his helmet lights, raised his Sun-visor and watched silently, surveying the stars and the thunderstorms which flashed over Lebanon and Israel. Wrapping up the final spacewalk of the mission at 5:06 p.m., STS-110 had seen a cumulative total of 28 hours and 32 minutes of EVA time, more than any previous shuttle-based ISS assembly mission. In fact, not until STS-123 in March 2008 would a shuttle assembly mission feature a greater amount of EVA time. Moreover, Ross and Smith established themselves in first and second place on the list of the United States’ most experienced spacewalkers.

Atlantis’ astronauts bade farewell to the Expedition 4 crew for the final time on 17 April and undocked from the space station at 2:31 p.m. EST, targeting a touchdown on the Shuttle Landing Facility (SLF) at the Kennedy Space Center (KSC) in Florida on the 19th. Blessed by near-perfect weather conditions—hampered only by scattered clouds—Bloomfield and Frick performed the de-orbit “burn” of Atlantis’ Orbital Maneuvering System (OMS) at 11:20 a.m. EST, committing them to an hour-long hypersonic descent to Earth. Returning home from her 25th flight, Atlantis alighted on Runway 33 at 12:27 p.m., closing out a mission of almost 11 days in duration.

This is part of a series of history articles, which will appear each weekend, barring any major news stories. Next week’s article will focus on the 45th anniversary of Apollo 16, the second-to-last piloted mission to the Moon.